An emulsion is simply a stable mixture of two or more immiscible liquids maintained by emulsifiers. The emulsions are characterized as having a continuous phase and a dispersed phase. In oil field terminology, an emulsion is a water-in-oil emulsion. An oil-in-water emulsion is called a reverse emulsion.
Reverse emulsions most commonly occur in secondary and tertiary oil recovery. For, in those types of recoveries, water, steam, surfactant or polymer are traditionally forced downhole to push oil out of the formation. In the process, the water mixes with the oil and is produced at the well-head along with the oil. This produced water is intimately mixed with the oil in the formation under pressure. Because of the pressure and mixing in the presence of surfactants or polymers, typically produced water is an oil-in-water emulsion; that is a reverse emulsion.
This reverse emulsion must be broken for at least two reasons. Typically, the water must be clarified before it can be sent to waste treatment systems. The water must also be clarified if it is to be recycled downhole for forcing more oil from the formation. In either of those two cases, failure to clarify the water by removing oil can result in serious problems. Most waste treatment facilities are not equipped to handle oil-in-water emulsions on the scale produced by an oil producing well. Moreover, if unclarified produced water is sent downhole, contaminants in the water can plug the formation.
Another reason to clarify the water by breaking the reverse emulsion is to reclaim the oil. The purpose of an oil recovery program is to produce oil for sale.